The Cuckoo Escapement: field report, kernel patch, dashboard

What the Raspberry Pi time-server guides get wrong on a Pi 4, with the
measurements. The headline artifact is a four-line pps-gpio patch: PREEMPT_RT
force-threads IRQ handlers, and pps-gpio takes its timestamp inside its handler,
so the realtime kernel puts a scheduler between the electrical edge and the
clock. IRQF_NO_THREAD takes RMS offset from 2468 ns to 199 ns.

- kernel/     the patch
- dashboard/  live status page (position hidden by default)
- docs-site/  the write-up (Astro/Starlight, brass, no tutorial section)

docs-site/.env.example

@@ -0,0 +1,9 @@
+# The Cuckoo Escapement — docs-site environment.
+# Note: no MODE var. The compose *profile* is the mode switch
+# (the warehacking reference doc is stale on this point).
+
+COMPOSE_PROJECT_NAME=cuckoo-escapement-docs
+
+# Production:  cuckoo.warehack.ing
+# Local dev:   cuckoo.l.warehack.ing   (internal only — never reference publicly)
+DOMAIN=cuckoo.warehack.ing